Geographic Range

Brown four-eyed opossums (Metachirus nudicaudatus) have a fairly large Central and South American range. These animals can be found as far north as southern Mexico, south into northeastern Brazil and Argentina, east into Guyana, French Guiana and Suriname and west into Peru and Ecuador. (Brito, et al., 2012; Gardner and Dagosto, 2008; Nowak, 2005)

Physical Description

Brown four-eyed opossums are medium-sized marsupials and the largest didelphid without a pouch. Their head and body length is 190 to 310 mm and their tails range from 195 to 390 mm. Sexual dimorphism is present in this species; in general, females are about 20 to 30 mm shorter than males. Males average 490 grams, females average 350 grams and the average overall body weight for the species is 460 grams. Their short, dense, silky dorsal pelage may vary based on their range, from reddish to yellowish-brown. Their dorsal fur often darkens as it approaches their rump and lightens on their sides. Their fur may have thin pale streaks along their dorsum. Ventrally, their pelage is yellowish or buffy brown. Brown four-eyed opossums have thin skulls with a long rostrum. Their face is dusky and blackish. They have whitish spots above each eye and a pale rostrum and pale cheeks. Brown four-eyed opossums also have a thick reddish-brown stripe encircling each eye, from their nose up to their hairless brown ears. Their dental formula is similar to other didelphids: 5/4, 1/1, 3/3, 4/4, with 50 teeth total. Their sparsely furred tail is longer than their head and body length and appears brownish, with a white tip. These animals also have whitish feet. (Gardner and Dagosto, 2008; Helder-Jose and Freymuller, 1995; Nowak, 2005; Reid, 2009; Richard-Hansen, et al., 1999; Smith, 2008)

Reproduction

There is currently very little information available regarding the mating systems of brown four-eyed opossums specifically. However, members of family Didelphidae are generally considered polygynous. Males from studied species compete for reproductive females. Generally, didelphids show neither courtship displays nor pair bonds. (Fernandes, et al., 2010; O'Connell, 2006)

Brown four-eyed opossums likely breed throughout the wet season, from October to April. These polyestrous animals probably have 2 litters annually. Lactating females have been captured throughout much of the year in February, April, May, June, September and October. Females with young have been found in February, April, June and October through December. Likewise, lone juveniles have been captured January through June and November. As this wide range in dates shows, there is still a great deal to be understood about the reproductive season in brown four-eyed opossums. Their litter sizes range from 1 to 9 offspring, with an average of 5 young per litter. Females do not have a pouch, but instead have a single lateral skin fold on their abdomen with 5, 7 or 9 mammae. (Bergallo, 1994; Brito, et al., 2012; Diaz and Flores, 2008; Gardner and Dagosto, 2008; Nowak, 2005; Smith, 2008)

Very little is known of the parental investment of brown four-eyed opossums. Females are believed to reproduce in the wet season and there have been reports of offspring associated with females throughout much of the dry season. After remaining attached to their mother’s mammae for a period of time, juvenile brown four-eyed opossums likely ride on their mother’s back during nightly excursions. (Bergallo, 1994; Diaz and Flores, 2008; Smith, 2008)

Behavior

Brown four-eyed opossums are solitary and terrestrial. Both males and females of this species create spherical nests of dry leaves and twigs in the forest litter and between tree roots. These animals are nocturnal; their peak activity occurs between 8 and 11 pm; after 2 am they do not show any activity. These animals may also increase their activity rate after a rainfall. Brown four-eyed opossums are cautious and anxious, they move quickly and run silently when disturbed, they are also less likely to be successfully trapped than other didelphids. (Brito, et al., 2012; Emmons, 1990; Gardner and Dagosto, 2008; Loretto, et al., 2005; Moraes Junior, 2004; Nowak, 2005; Reid, 2009)

Communication and Perception

Brown four-eyed opossums are generally quiet animals; however, when they perceive a threat they may click or gnash their teeth and hiss. A cornered female with young has been observed pulsating her body against her leafy nest, which gave her the appearance of a much larger animal. Due to her young, her ability to run quickly may have been impaired. These animals also have 2 paracloacal scent glands, which are larger in males. Generally, didelphids also have good eyesight and hearing, although these specific sensory functions have not been reported for brown four-eyed opossums. (Gardner and Dagosto, 2008; Helder-Jose and Freymuller, 1995; Loretto, et al., 2005; O'Connell, 2006)

Economic Importance for Humans: Positive

There are currently no known positive impacts of brown four-eyed opossums on human populations.

Economic Importance for Humans: Negative

Brown four-eyed opossums are occasionally blamed for the destruction of crops. (Nowak, 2005)

Negative Impacts

crop pest

Conservation Status

Currently, brown four-eyed opossums are considered a species of least concern according to the IUCN Red List of Threatened Species. These animals are likely widespread but rarely seen, they may have a large population and they are found in a variety of protected areas. (Brito, et al., 2012; Reid, 2009)

Other Comments

Due to the physical variations of this species in different ranges, it has been suggested that what is known as one species may in fact be several. Currently, brown four-eyed opossums have 5 recognized subspecies including M.n columbianus, M.n. modestus, M.n myosuros, M.n nudicaudatus and M.n tschudii. (Brito, et al., 2012; Gardner and Dagosto, 2008; Miranda, et al., 2009)

Contributors

Leila Siciliano Martina (author), Animal Diversity Web Staff.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

omnivore

an animal that mainly eats all kinds of things, including plants and animals

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Bergallo, H. 1994. Ecology of a small mammal community in an Atlantic forest area in southeastern Brazil. Studies on Neotropical Fauna and Environment, 29:4: 197-217.

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.